This circuit amplifies the input without inverting it, multiplying the voltage by 3, using an
op-amp.
The op-amp attempts to keep its two inputs at the same voltage.
One is at the input voltage, so for the other one to be the same, there must
be a voltage drop across the 1k ohm resistor equal to the input
voltage. The 2k ohm resistor has the same current across it so the
voltage drop must be twice as large, by
Ohm's Law. So the
output voltage is equal to the input plus 2x the input, or a total of
3x the input.